An example of the power source device of this kind has been disclosed in Japanese Patent Laid-Open Publication No. 2-282809, in which the power source devices comprise, as shown in FIG. 24, a boosting chopper circuit for improving the input current distortion by means of switching elements Q1 and Q2, inductor L1 and diodes D5 and D6, and a buck converter for limiting a load current by means of switching elements Q1-Q4 and inductor L2.
Referring more specifically to FIG. 24, there are connected, in parallel to a smoothing capacitor C, series connections respectively of diodes D1 and D2, of diodes D3 and D4, of the diodes D5 and D6, of the switching elements Q1 and Q2 and of the switching elements Q3 and Q4. A junction point between the switching elements Q1 and Q2 and a junction point between the diodes D1 and D2 are connected. Further, a junction point between the switching elements Q3 and Q4 and junction point between the diodes D3 and D4 are connected. Between the junction point of the switching elements Q1 and Q2 and the junction point of the switching elements Q3 and Q4, a series connection of the inductor L2 and a load Z is connected. Between the junction point of the diodes D5 and D6 and the junction point of the switching elements Q1 and Q2, a series connection of an AC power source P through a filter circuit F to the inductor L1 is connected.
In this case, a control circuit (not shown) is controlling ON/OFF operation of the switching elements Q1-Q4 with outputs ON/OFF signals to gate electrodes of the switching elements Q1-Q4, so that, in positive half cycles of AC source power, the switching element Q1 is alternately made ON and OFF, the switching elements Q2 and Q3 are made OFF and the switching element Q4 is made ON. In negative half cycles, on the other hand, the switching element Q2 is alternately made ON and OFF, the switching elements Q1 and Q4 are made OFF and the switching element Q3 is made ON.
The operation of the conventional device of FIG. 24 shall be described with reference to FIG. 25. First, when the AC power source P is in the positive half cycle so that the switching elements Q1 and Q4 are ON and the switching elements Q2 and Q3 are OFF, a current flows, as shown in FIG. 25a, through a path of the AC power source P, filter circuit F, diode D5, switching element Q1 and inductor L1, to have an energy accumulated in the inductor L1. Also, a current flows from the smoothing capacitor C through a path of the switching element Q1, inductor L2, load circuit Z and switching element Q4 to cause a voltage at the smoothing capacitor C dropped by the inductor L2 and supplied to the load circuit Z. Further, with the current flowing to the inductor L2, an energy is accumulated in the inductor L2.
Next, as the switching element Q1 only is made OFF, a voltage is generated across the inductor L1 by the accumulated energy in the inductor L1, and this voltage is charged through the diode D2 in the smoothing capacitor C as superposed on a voltage of the AC power source P. That is, as shown in FIG. 25b, a current flows through a path of the AC power source P, filter circuit F, diode D5, smoothing capacitor C, diode D2 and inductor L1, to cause the energy in the inductor L1 discharged. Due to this, there is always flowing a current of high frequency from the AC power source P, and any input current distortion is improved by shaping the waveform of the current by means of the filter circuit F. At the smoothing capacitor C, further, there is obtained a voltage higher than a peak value of the AC power source P. Still further, a regenerative current owing to the accumulated energy in the indutor L2 flows through a path of the inductor L2, load circuit Z, switching element Q4 and diode D2. Thereafter, the operation of FIGS. 25a and 25b is repeated as a result of the turning ON and OFF at a high frequency of the switching element Q1, and a DC voltage in one direction is supplied to the load circuit Z.
Next, in the negative half cycle of the AC power source P in which the switching elements Q1 and Q4 are OFF and the switching elements Q2 and Q3 are ON, a current flows, as shown in FIG. 25c, through a path of the AC power source P, filter circuit F, inductor L1, switching element Q2 and diode D6, and an energy is accumulated in the inductor L1. From the smoothing capacitor C, further, a current flows through a path of the switching element Q3, load circuit Z, inductor L2 and switching element Q2, to cause the voltage at the smoothing capacitor C dropped by the inductor L2 and supplied to the load circuit Z. Still further, with the current flowing to the inductor L2, an energy is accumulated in the inductor L2.
Next, as the switching element Q2 only is made OFF, a voltage is generated across the inductor L1 by the accumulated energy in the inductor L1, and this voltage is charged in the smoothing capacitor C through the diode D1 as superposed on the voltage of the AC power source P. That is, as shown in FIG. 25d, a current flows through a path of the AC power source P, filter circuit F, inductor L1, diode L1, smoothing capacitor C and diode D6, and the energy in the inductor L1 is discharged. Due to this, there is always flowing a current of high frequency from the AC power source P, and any distortion in the input current is improved by shaping the waveform of the current by means of the filter circuit F. At the smoothing capacitor C, further, there is obtained a voltage higher than the peak value of the AC power source P. Still further, a regenerative current owing to the accumulated energy in the inductor L2 flows through a path of the inductor L2, diode D1, switching element Q3 and load circuit Z. Thereafter, the operation of FIGS. 25c and 25d is repeated as a result of the turning ON and OFF at a high frequency of the switching element Q2, and a reverse directional DC voltage is supplied to the load circuit Z. With the foregoing operation, a square wave voltage of the polarity inverting in synchronism with every half cycle of the AC power source P is supplied to the load circuit Z.
In the positive half cycles of the AC power source, as has been described, the switching element Q1 operates concurrently as a switching element of a chopper circuit and as a switching element of an inverter circuit. In the negative half cycles of the AC power source, on the other hand, the switching element Q2 operates concurrently as the switching element of the chopper circuit and as the switching element in the inverter circuit.
As another conventional example, there may be shown in FIG. 26 a power source device, which comprises a boosting and dropping chopper circuit for improving the input distortion by means of the switching elements Q1 and Q2, inductor L1 and diodes D1, D2 and D5-D10, and a buck converter for limiting the load current by means of the switching elements Q1-Q4 and inductor L2. In this case, a series circuit of the diodes D1 and D2 and a series connection of the diodes D3 and D4 are connected in inverse parallel to the smoothing capacitor C, and a series connection of the switching elements Q3 and Q4 are connected in parallel to the smoothing capacitor C. A series connection of the diodes D5 and D6 and a series connection of the switching elements Q1 and Q2 are connected in inverse parallel, and a circuit of a series connection in the order of the diode D7, switching elements Q1 and Q2 and diode D8 and a series circuit of the diodes D9 and D10 are connected in inverse parallel to the smoothing capacitor C. Further, a junction point between the diodes D1 and D2 and a junction point between the switching elements Q1 and Q2 are connected, and a junction point between the diodes D3 and D4 and a junction point between the switching elements Q3 and Q4 are connected. Still further, the inductor L1 is connected between the junction point of the switching elements Q1 and Q2 and a junction point of the diodes D9 and D10, a series connection of the inductor L2 and load circuit Z is connected between the junction point of the switching elements Q1 and Q2 and the junction point of the switching elements Q3 and Q4, and the AC power source P is connected between a junction point of the diodes D5 and D6 and the junction point of the diodes D9 and D10.
Referring further to this power source device with reference to FIG. 26 and additionally to FIG. 27, initially in the positive half cycle of the AC power source P in which the switching elements Q1 and Q4 are ON and the switching elements Q2 and Q3 are OFF, a current flows, as shown in FIG. 26a, through a path of the AC power source P, filter circuit F, diode D5, switching element Q1 and inductor L1, and an energy is accumulated in the inductor L1. Further, a current flows from the smoothing capacitor C through a path of the diode D7, switching element Q1, inductor L2, load circuit Z and switching element Q4, and a voltage at the smoothing capacitor C is supplied to the load circuit Z as dropped by the inductor L2. Also, with the current flowing to the inductor L2, an energy is accumulated in the inductor L2.
When the switching element Q1 only is made OFF, next, a voltage is generated across the inductor L1 by the accumulated energy in the inductor L1, and is charged through the diode D9 in the smoothing capacitor C. That is, as shown in FIG. 26b, a current flows through a path of the inductor L1, diode D9, smoothing capacitor C, diode D2 and inductor L1, and the energy in the inductor L1 is discharged. Due to this, the current from the AC power source P is caused not to flow directly to the smoothing capacitor C, but the current once made to flow to the inductor L1 is accumulated therein as the energy, and a regenerative current owing to such accumulated energy is caused to flow to the smoothing capacitor C, so that any rush current upon connection of the AC power source P can be prevented. At the smoothing capacitor C, further, a voltage lower than the peak value of the AC power source P can be obtained. Further, a regenerative current owing to an accumulated energy in the inductor L2 flows through a path of the inductor L2, load circuit Z, switching element Q4 and diode D2. Thereafter, the operation of FIGS. 26a and 26b is repeated by the high frequency ON/OFF operation of the switching element Q1, and the DC voltage in one direction is supplied to the load circuit Z.
Next, in the negative half cycle of the AC power source P in which the switching elements Q1 and Q4 are OFF and the switching elements Q2 and Q3 are ON, a current flows, as shown in FIG. 27a, through a path of the AC power source P, filter circuit F, inductor L1, switching element Q2 and diode D6, and an energy is accumulated in the inductor L1. Also, a current flows from the smoothing capacitor C through a path of the switching element Q3, load circuit Z, inductor L2, switching element Q2 and diode D8, and the voltage at the smoothing capacitor C is supplied to the load circuit Z as dropped by the inductor L2. Also, with the current flowing to the inductor L2, an energy is accumulated in the inductor L2.
When the switching element Q2 only is made OFF, next, a voltage is generated across the inductor L1 by the accumulated energy in the inductor L1, and is charged in the smoothing capacitor C through the diode D1. That is, as shown in FIG. 27b, a current flows through a path of the inductor L1, diode D1, smoothing capacitor C and diode D10, and the energy in the inductor L1 is discharged. The current from the AC power source P is thereby caused not to flow directly to the smoothing capacitor C, and the current flowing to the inductor L1 is once accumulated therein as the energy, and the regenerative current owing to this accumulated energy is made to flow to the smoothing capacitor C, so that any rush current upon connection of the AC power source P can be prevented. Further, there can be also obtained at the smoothing capacitor C a voltage lower than the peak value of AC power source P. Further, a regenerative current owing to the accumulated energy in the inductor L2 flows through a path of the inductor L2, diode D1, switching element Q3 and load circuit Z. Thereafter, the operation of FIGS. 27a and 27b is repeated by the high frequency ON/OFF operation of the switching element Q2, and a DC voltage in reverse direction is supplied to the load circuit Z. With the foregoing operation, a square wave voltage of the polarity inverting in synchronism with every half cycle of the AC power source P is supplied to the load circuit Z.
In the conventional example of FIGS. 24 and 25, however, the switching elements are used commonly in the boost converter and the buck converter so that the currents of both buck-boost converters are caused to flow as superposed to the commonly used switching elements, the withstand amount of current is enlarged, and any effect of cost reduction attained by reducing the number of the switching elements through the common use is rather decreased. Further, as the control signals for the switching elements are also used in common, the independence of control with respect to each circuit is lost so that, in an event where the control is to be made for rendering an output power constant, for example, there arises an instance where an input power is excessively over or below the output power. When the input power is excessively over the output power, a surplus energy is accumulated in the smoothing capacitor so as to raise the voltage across the smoothing capacitor, the voltage applied to the parts is increased, and there arises a problem that a stress is given to the parts according to circumstances.
Such phenomenon becomes particularly remarkable in an event where the conventional device is applied to, for example, a starting device of a high pressure discharge lamp because, in the step of starting the high pressure discharge lamp, the load is low in the impedance and it becomes necessary to supply a large current to the load. That is, there must be provided a constant ON duty in order to let the large current flow to the load but, as the load is low in the impedance, the output power is less. In contrast, the input power will be of an amount in accordance with the ON duty, and there arises a problem that the input power becomes excessively large.
Further, in the conventional example of FIGS. 26 and 27, there are advantages that the voltage of the smoothing capacity is enabled to be set lower than the source voltage, and further any rush current upon connection of the power source can be prevented, since the switching elements are used commonly in both buck-boost converters and buck converters. However, because of the increase in the withstand amount of current of the commonly used switching elements as being the problem in the conventional example of FIGS. 24 and 25, there are problems that a cost reduction is difficult to be contrived, and the independence of control with respect to every circuit is also difficult to be maintained.